Java:不兼容的类型

Question

import java.text.*;
import java.util.*;
public class Proj3 {
    public static void main(String[]args){
     // DecimalFormat df = new DecimalFormat("#0.00”);
     Scanner s = new Scanner(System.in);
     int TotalHours = 0;
     int TotalGrade = 0;

     System.out.print("How many courses did you take? ");
     int Courses = Integer.parseInt(s.nextLine());
     System.out.println("");

     int CourseNumber = Courses - (Courses - 1);
     while (Courses > 0){
         System.out.print("Course (" + CourseNumber +"): How many hours? ");
         int Hours = Integer.parseInt(s.nextLine());
         TotalHours = TotalHours + Hours;

         System.out.print("Course (" + CourseNumber +"): Letter grade? ");
         char Grade = s.nextLine().charAt(0);

         if (Grade == 'A'){
             TotalGrade = TotalGrade + (4 * Hours);
            }
         if (Grade == 'B'){
             TotalGrade = TotalGrade + (3 * Hours);
            }
         if (Grade == 'C'){
             TotalGrade = TotalGrade + (2 * Hours);
            }
         if (Grade == 'D'){
             TotalGrade = TotalGrade + (1 * Hours);
            }

         Courses = Courses - 1;
         CourseNumber = CourseNumber + 1;
        }
     Double GPA = TotalGrade / TotalHours;
     System.out.println(df.format(GPA));

    }
}

这是一项作业，我不知道如何解决我的问题。Double GPA = TotalGrade/ToutalHours; 行出现了 Incompatible Types 错误。

另外，我应该在主程序的开头包含 DecimalFormat df = new DecimalFormat("#0.00”); 行，但它不起作用。

任何事情都非常有帮助。谢谢

Answer 1

 Double GPA = TotalGrade / TotalHours;

Autoboxing是 Java 编译器在原始类型和它们相应的对象包装器类之间进行的自动转换。因此 Double 是原语 double 的包装类，Integer 是原语 int 的包装类。

您的 TotalGrade/TotalHours 生成的是 int，但您试图将其分配给类型为 Double 的对象。执行以下任一操作:

double GPA = (double)TotalGrade / TotalHours;

或者，

Double GPA = (double)TotalGrade / TotalHours;